Oscillating heterodyne detector



April 28, 1931.

J. M. GRIGG 1,803,247

OSCILLATING HETERODYNE DETECTOR Filed Sept. 10, 1928 M A g g 5 L4 5 o o o i -7 g 0 17 o o o O E; 5 g o a 5 0 g g o g o o H- i II INVENTOR ATTORNEY Patented Apr. 28, 1931 UNITED STATES PATENT OFFICE Jesse M. same, or onroeeo, ILLINOIS oscmLA'rme HErnnoDYNE nrl'rEc'ron Application filed September 10, 1928. Serial No. 305,035.

This invention relates to radio receiving apparatus and clrcuits and has forits general ob ect the provision of an oscillating heterodyne.detector circuit adapted to be interposed between any desired number of stages of radio frequency amplification and any desired number of stages of intermediateor beat frequency amplification.

The most important object of the invention is to provide a detector circuit embodying a resonant circuit inductively coupling the grid and plate circuits of the detector tube inwcontradistinction to providing an actual,

direct or metallic connection.

Another important object of the invention is to provide a resonant circuit'in whichvoscillation is sustained through the agency of the resonant system in action as" relay in the inductive-transfer of energy from the plate Lircuit to the grid circuit.

Another object of the invention is to provide an oscillating system comprising'a reso nant coil, a grid coil, and a plate coil, the resonant coil being both'interpos ed between the grid coil and the plate coil and coupled to these in proper degree and direction of mutual inductance; and all three coils therefore being in such combined relationship that'the electro-motive force relayed or transferred -'.1o the grid coil through the agency of the resonantcoil exceeds the electroinotive force of direct induction byan amount su'fiicient to sustain oscillation. v i

Another object of the invention is to pro- 'ride a circuit of this character in which the arrangement is such that the input in series with the grid circuit or coils insures maiiimum transfer of potential,this input having one'en'd at low potential, in fact atfilament potential, therefore picking up only a minimum of stray capacitive energy and avoid-g ing undesirable bod capacity efiect.

Another objector the invention is "to provide a circuit of this character in whichthe provision of a high plate potential and a corresponding proper'negative grid bias will keep the grid damping down;

Another object of theinvention is to'prok vide acircuit'wherein-the beat frequency is rectified into the system and in which a certain predetermined frequency, suchas that in the ordinary wave band for broadcast reception may be heterodyned to an intermepreferably consists in the circuit arrangement to be hereinafter more fully described and claimed,, and illustrated in the accompanying drawingin which: i i

The figure is adiagram of. the complete circuit arrangement. j

Referring more particularly to the draw tector circuits in whichthe numeral 10 desiging, I have illustrateda combinationof denates a detector tube having a grid 11, filament 12, and aplate 1 3. g

There is nothing distinctive about the tube and itmay be one of various types .on the market for the purpose. Thefilament 12, isiofcourse, intended to be heated by means ofa suitable source .of-A, current, regulation being efiected by means of a suitable rheostat 14.. The battery, or its equivalent, is. not illustrated, inasmuch as it is well known. The circuitfurther includes induc tances L1, L2, L3, L4, and L5. The indu'c tanceLljmay be the secondary of a radiofref- 'quenc y transformer 15 embodying the induc:

tance L, or'it" may be a loop or' other device,

there being no particular limitations in this respect.

' The inductance L1 is shunted by a variable condenser Cl and is connected in series between the negative terminal of the A battery and the grid inductance L3 as clearly shown in the diagram. As it is desirable that the proper negative bias be applied to the grid lead, there is disclosed, diagrammatically, a C battery 16 interposed in series between the inductance L1 and the negative terminal of the A battery as is customary. The inductance L2 is shunted by a variable condenser C2 and is of course, connected with the negative terminal of the A battery as indicated. The inductance L4 is connected in series between the plate 13 of the tube 10 and the inductance L5 of" the output, the

latter being, of course, connected with the positive terminal of the source of B current. The inductance L5 is shunted by a bypass condenser 17 and there is also provided a by-pass condenser 18 between the negative terminal of the A battery and the positive terminal of the B battery as is likewise customary. V

The inductance L5 may be the primary coil of an intermediate frequency amplifier 19 or any other equivalent device, this being totally immaterial. The point is that there must be an output, and in. a multiple stage circuit it is customary to provide two or more stages of intermediate frequency amplification of which the transformer 19 mayconstitute the first one. 7

In considering the entire detector circuit it will be noted that essentially it contains the resonant circuit C2, the inductance or coil L2 of which is inductively interposed between the grid coil L3 and the plate coil L4.

It is intended that the windings of the free ends of the, coils. be in opposite directions. In theory, the plate coil L ttransfers its energy to the resonant coil L2, which in turn induces an electro-motive force in the grid coil L3 and sustains oscillation. The input L1 in series with the grid coil L3 insures maximum transfer of potential, and with its low potential end at filament potential picks ,up a minimum of stray capacitive energy.

A high plate potential and corresponding negative grid bias keepthegrid damping ate frequency. just below the broadcast band,

or a difference between signaland oscillator frequency of about 500,00'( )-1cycles, the use of. whichfrequency, as is well known,results in a one-spotsuper-heterodyne. Actually I'havebuilt two successful receivers using this type of frequency-changer. on'e emnlo'ving the second harmonic principle and a beat frequency of kilo-cycles, and the other using the first harmonic principle and a beat frequency of 500 kilo-cycles, showing that satisfactory operation may be had in any practical case, that is to say where loop and oscillator are not tuned too near to the same frequency.

Incidently, the amplifiers employed in both the receivers may be of an ordinary or of a preferred type capable of individual and characteristic construction.

The advantages of this frequency changer are that the faults found in other types of one tube arrangements are absent. As near as can be determined, there is no reaction between the two tuned circuits, and since the rotors of both condensers are at filament potential.

In conclusion, it may be said that inasmuch as I have experimented with all the well known types of frequency changers, besides several others of my own: devising,..th e arrangement disclosed herein appears from every angle to be the most satisfactoryof all. It is thought from the foregoing that the construction, operation and advantages will be readily apparent to one skilled in the art without further explanation.

lVhile I have shown anddescribed the preferred embodiment of the invention, it should of course, be understood that various modifications may beresorted to without in any way departing from the spirit of the inventure fromthe scope of the subjoined claims.

Having thus described my invention, I

claim:-

1 In a stage of radio detection, an input inductance, an output inductance, a vacuum tube,-a grid inductance connected in series with said inputinductance and the grid of the vacuum tube, a plate inductance connected in series between the plate of the vacuum tube and the said-output inductance, means for tuning said grid inductance, and an intermediate circuit embodying an inductance inductively coupled to said grid inductance and said plate inductance and having tuning means associated therewith for-controlling local oscillations at a different frequency from the impulses inthe grid circuit whereby heterodyning maybe accomplished with ya single'vaeuumtube.

2. In astageof detection, the

combination of an input circuit, an output circuit, a grid circuit coupled to the input circuit and connected with the grid of a vacuum tube, an inductance connected in said grid circuit between the input circuit and the grid, an inductance connected with the plate of the tube and connected with'the output circuit, and an intermediate resonant circuit embodying an inductance inductively coupled to the plate 0 inductance and the grid inductance.

In testimony whereof I aflix my signature.

JESSE M. GRIGG. 

